Markings for aligning fiber optic bundle

ABSTRACT

A lithographic process is used to place a marking on a waveguide to indicate optical channels within the waveguide. A photonic component is positioned against the waveguide based on the markings and adjusted until aligned.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The described invention relates to the field of optics. Inparticular, the invention relates to alignment and coupling of photoniccomponents.

[0003] 2. Description of Related Art

[0004] Photonic components propagate light and include waveguides,optical fibers, amplifiers, couplers, splitters, and other devices forcarrying light-based signals. A fiber optic bundle has multiple opticalfibers for propagating light, and an array waveguide (AWG) has multiplechannels for propagating light within. Coupling a fiber optic bundle toan AWG, for example, is not easy. Manual alignment requires detectingand maximizing light connectivity between the fiber optic bundle and theAWG. Once a good connection is obtained, permanently fixing thealignment is required.

[0005]FIG. 1A shows a prior art fiber optic bundle 10. The fiber opticbundle 10 comprises multiple optical fibers 12 sandwiched between tworetainers 16 and 18. The retainers are substrates made of silicon, forexample, that are appropriately masked with a suitable etch mask.Thereafter, symmetrically spaced unmasked areas of the substrate areexposed to a chosen anisotropic etchant, such as hot KOH orethylenediamine. This etchant preferentially attacks a chosen (100)crystallographic plane of the silicon substrate and preferentiallyetches in a vertical direction until V-shaped grooves (“V-grooves”) areattained. Upon completion of these V-shaped grooves, optical fibers areplaced in the grooves and come to rest in alignment with the center ofthe V-grooves between the retainers 16 and 18.

[0006]FIG. 1B shows a prior art single retainer without the opticalfibers. The two retainers 16 and 18 form a termination block for thefiber optic bundle by sandwiching the optical fibers together withintheir V-grooves 24. The termination block maintains the spacing betweenthe optical fibers and allows for easily handling the fiber opticbundle. The ends of the optical fibers 22 are typically polished afterbeing set in the termination block.

[0007]FIG. 2 shows a prior art example of an AWG. The AWG comprisesmultiple channels 30 running through the AWG. The AWG may comprise aglass, silicon, oxide or polymer substrate. The channels are made ofmaterials having a higher index of refraction than the rest of the AWG.AWGs and fiber optic bundles may be made with various numbers ofchannels.

[0008]FIG. 3 shows a side view of a fiber optic bundle being aligned toan AWG 42. The optical fibers of the fiber optic bundle and the channelsof the AWG 42 have identical spacings and number. A dotted line 45 showsthe channels in the AWG. An epoxy 50 is used to hold the terminationblock 40 of the fiber optic bundle to the AWG 42, but alignment mustfirst be achieved and then maintained. It is difficult to achievealignment, i.e., photonically couple the optical fibers to the AWGchannels, and then to epoxy without losing alignment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1A shows a prior art fiber optic bundle

[0010]FIG. 1B shows a prior art single retainer without the opticalfibers.

[0011]FIG. 2 shows a prior art example of an AWG.

[0012]FIG. 3 shows a side view of a fiber optic bundle being aligned toan AWG.

[0013]FIG. 4 shows a first embodiment for aligning a fiber optic bundleto an AWG.

[0014]FIG. 5 shows a flowchart for aligning a photonic component to awaveguide.

DETAILED DESCRIPTION

[0015] One of the issues with aligning a photonic component with anarray waveguide is that the channels of the array waveguide are notvisible. Although the channels have a higher index of refraction thanthe surrounding substrate, they are not readily distinguishable by thehuman eye.

[0016]FIG. 4 shows one embodiment for aligning a fiber optic bundle 140to an array waveguide (AWG) 142. Markings 160 are placed on a surface ofthe waveguide 142 indicative of the channels 145 within the waveguide142. The markings 160 are lithographically-defined, i.e., they areplaced on the waveguide during the lithographic processing of thewaveguide, and they precisely indicate the location of the channels 145.In one embodiment, an ‘X’ marking may indicate the center of a channeldirectly beneath it. In another embodiment, markings may indicate theoutside boundaries of an interior channel. In one embodiment, markingsare placed over the outermost channels of the waveguide 142, however,the markings can be placed over any of the channels 145.

[0017] The markings may be achieved by etching into the substrate of thewaveguide, by placing ink on a, e.g., passivation layer, or by any othertechnique that produces a marking that is visible to the human eye.

[0018] The fiber optic bundle may have alignment markings 172 of itsown. Thus, viewed from the top it would be easy to line up the markings160 of the waveguide to the alignment markings 172 of the fiber opticbundle 140. Alternatively, the tops of V-grooves 170 may be used toalign the fiber optic bundle 140 to the markings 160 of the waveguide142.

[0019] In another embodiment, marking 190 on the side surface of thewaveguide 142 may be used to indicate a depth of the channels 145 withinthe waveguide 142. As an example, a marking 190 on the side of thewaveguide may be achieved by deposition of a layer of material having adifferent color than the rest of the substrate. This layer may belimited to the side surfaces of the waveguide 140.

[0020]FIG. 5 shows a flowchart for aligning a photonic component to awaveguide. The flowchart starts at block 200 and continues at block 202,at which the photonic component, such as a fiber optic bundle, is placedagainst the waveguide. At block 204, the photonic component is alignedto the lithographically-defined markings on the waveguide. In oneembodiment, the markings on the photonic component are used to help withcourse alignment with the markings on the waveguide. Some type ofoptical measuring device may be needed to help with fine alignment byoptimizing the optical coupling between the photonic component and thewaveguide. At block 206, the photonic component is bonded to thewaveguide. In one embodiment, an epoxy having an index of refractionthat is substantially similar to the channels of the waveguide and tothe optical fibers of the fiber optic bundle is used to help maintainthe optical coupling between the waveguide and the photonic component.

[0021] Thus, a method and apparatus for aligning a photonic componentwith a waveguide is disclosed. However, the specific embodiments andmethods described herein are merely illustrative. Numerous modificationsin form and detail may be made without departing from the scope of theinvention as claimed below. For example, although a fiber optic bundlealigned to a waveguide was described, the same process can be used foraligning other photonic components, such as aligning two waveguides toeach other. The invention is limited only by the scope of the appendedclaims.

What is claimed is:
 1. A method of coupling a photonic component with awaveguide comprising: positioning the photonic component against thewaveguide; and aligning the photonic component with markings that havebeen lithographically-placed on a surface of the waveguide.
 2. Themethod of claim 1, wherein the photonic component is a fiber opticbundle.
 3. The method of claim 2 further comprising: aligning outermostoptical fibers of the fiber optic bundle with the markings on thesurface of the waveguide.
 4. The method of claim 3 further comprising:bonding the fiber optic bundle to the waveguide.
 5. The method of claim1, wherein the photonic component is a second waveguide.
 6. A method ofaligning a fiber optic bundle with a waveguide comprising: using alithographic process to place a marking on a surface of the waveguide,the marking indicative of an optical channel within the waveguide;positioning the fiber optic bundle against the waveguide based on themarking; and adjusting the fiber optic bundle until alignment isachieved.
 7. The method of claim 6 further comprising: using thelithographic process to place a second marking on the surface of thewaveguide, the second marking indicative of a second optical channelwithin the waveguide, wherein the positioning of the fiber optic bundleagainst the waveguide is also based on the second marking.
 8. The methodof claim 7, wherein the lithographic process uses an etch to place thefirst and second markings.
 9. The method of claim 7, wherein thelithographic process uses an ink to place the first and second markings.10. The method of claim 7, wherein the lithographic process deposits alayer of material that is distinguishable by the human eye to place thefirst and second markings.
 11. The method of claim 7, wherein themarking is directly above the optical channel.
 12. The method of claim7, wherein the marking is lateral to the optical channel.
 13. The methodof claim 7, wherein the positioning of the fiber optic bundle againstthe waveguide is also based on alignment markings on the fiber opticbundle.
 14. The method of claim 13 further comprising: applying an epoxybetween the fiber optic bundle and the waveguide.
 15. A waveguidecomprising: a first optical channel within the waveguide; and a firstlithographically-defined marking on a surface of the waveguideindicative of the first optical channel within the waveguide.
 16. Thewaveguide of claim 15 further comprising: a second optical channelwithin the waveguide; and a second lithographically-defined marking onthe surface of the waveguide indicative of the second optical channelwithin the waveguide.
 17. The waveguide of claim 16, wherein the firstlithographically-defined marking and the second lithographically-definedmarking are directly above the first optical channel and the secondoptical channel, respectively.
 18. The waveguide of claim 17, whereinthe first lithographically-defined marking and the secondlithographically-defined marking are at an edge of the waveguide. 19.The waveguide of claim 18, wherein the waveguide comprises glass. 20.The waveguide of claim 18, wherein the waveguide comprises silicon. 21.The waveguide of claim 18, wherein the first optical channel and thesecond optical channel are on opposite sides of the waveguide.